The present invention relates to a control apparatus for an automatic transmission of a motor vehicle, and a method of controlling an automatic transmission of a motor vehicle.
Recently, there is a growing demand on more precision and finer control of the shift characteristic of an automatic transmission.
There is known a control apparatus for an automatic transmission which employs a microcomputer based controller. The controller stores data in the form of maps relating to various kinds of shift patterns including a power pattern where an acceleration performance is emphasized and an economy pattern where a fuel economy is emphasized. Sensor output signals from a throttle sensor and a vehicle speed sensor are supplied to the controller. Based on the sensor signals, the controller performs a select operation among the above-mentioned maps and then a table look-up operation of the map selected to retrieve transmission ratio data arranged in the map versus throttle opening degree and vehicle speed to obtain a transmission ratio fit to a set of a throttle opening degree and a vehicle speed indicated by the sensor signals. The controller generates a shift signal indicative of the transmission ratio obtained. In this manner, a fine selection among transmission ratios is made to determine a transmission ratio most suitable for a running state which an automobile is involved in, since there are provided various shift patterns as mentioned above.
With the known control system, the plurality of maps are provided and selected in accordance with various running states which the automobile may be involved in, and there occur events where a shift between transmission ratios is made in accordance with an inappropriate shift schedule which is not fit to the running state of the vehicle. This is where an improvement is to be made. If all shift points fit for all available running states of the vehicle were to be set, the number of maps would be considerably increased. Therefore, it is the common practice to limit the number of shift patterns, each fit to one of representative running conditions.
Applicant of the present application has proposed in a copending U.S. patent application Ser. No. 07/175,350 filed on Mar. 30, 1988, now U.S. Pat. No. 4,841,815, a fuzzy-logic controlled automatic transmission. According to this previously proposed control, a fuzzy-logic is used in order to determine a transmission ratio suitable for vehicle running conditions. In the fuzzy-logic controller, a series of membership functions are referred to based on a series of signals representive of the running conditions. The membership functions are fixed once they are set, so that it is impossible to provide a shift characteristic with a sufficient flexibility to cope with different driver's driving behaviours and different environments which the motor vehicle may be involved in.
Therefore, an object of the present invention is to improve a control apparatus for an automatic transmission such that a shift characteristic in the automatic transmission is flexible enough to cope with different driver's driving behaviours and different environments which the motor vehicle may be involved in.